A hoop-like device intended to be wrapped around a limb or digit and used in conjunction with a limb plethysmograph (not included) to determine volume variations in the extremities (e.g., legs, toes, arms, fingers) as modified by the circulation of blood through them. Often referred to as a strain gauge, it typically operates based on electrical resistance changes with length, and is used during assessment of a variety of clinical conditions (e.g., endothelial dysfunction, reactive hyperemia, deep vein thrombosis) and for a number of techniques (e.g., arterial inflow, venous capacitance, maximum venous outflow), often with rapid cuff inflation devices. This is a reusable device.